There are numerous medicament delivery devices that have been invented and developed during the years. These devices have been provided with different degrees of functionality and automatic features, such as mixing of medicament components, priming, dose delivery, penetration, just to mention a few.
Many devices are arranged with an elongated plunger rod that acts on stoppers inside a medicament container. The plunger rod is pushed in the distal direction by drive force members that often are spiral compression springs. This configuration means that the device becomes quite long since the spring acts on a distal end of the plunger rod, a so called pen injector.
In many instances the users do not want these elongated pen-type injectors due to their form, and a few attempts have been made to shorten the length of the injector. In the design disclosed in U.S. Pat. No. 4,313,439 the size of the device is the linear dimension of the barrel, the piston rod and the linear dimension of the curved path of the spring-powered spheres, thus resulting in no reduction of the overall size. One alternative design is disclosed in U.S. Pat. No. 5,261,882 disclosing a negator spring powered I.V. pump of compact size resulting from imparting a non-circular, rather than a linear configuration to the negator spring; wherein the non-circular configuration takes up less size or linear dimension. However, the non-linear compartment for said negator spring comprises a first axle member establishing a rotating axis for a centrally disposed circular-shaped spindle having a peripheral surface for supporting movement therealong of plural interconnected spheres serving as a piston rod, and a second axle member establishing a rotating axis for a centrally disposed spool which supports the helical coils of the negator spring; thus also resulting in no optimal reduction of the overall size.